This application claims the benefit of Korean Application No. 98-24154, filed Jun. 25, 1998, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an apparatus and method for generating a tracking error signal, and more particularly, to an apparatus and method for adaptively generating a tracking error signal according to a phase error generated due to an irregular pit depth of a disk.
2. Description of the Related Art
A tracking servo of an optical disk is usually controlled by a differential phase detection (DPD) method of detecting a phase difference using a four-element optical detector.
FIG. 1 shows a tracking error signal extraction system using the DPD method. As shown in FIG. 1, an optical detector 10 includes four elements A, B, C and D which detect light beams reflected by an optical disk. Among optical detection signals output by the four elements A, B, C and D, the outputs of two elements diagonally located in a track direction are synthesized and applied to a differential amplifier 15. That is, when diagonal synthesized signals are A+D and B+C, the synthesized signal A+D is input to a (+) port of the differential amplifier 15, and the synthesized signal B+C is input to a (xe2x88x92) port thereof. Thus, an output signal of the differential amplifier 15 is (A+D)xe2x88x92(B+C).
FIGS. 2A through 2D illustrate phase relationships between optical detection signals obtained from the elements A through D, respectively, when an optical disk having a uniform pit depth is scanned in a radial direction.
Generally, the optical detection signals output by the elements A and C have the same phase, and likewise for signals output by the elements B and D, whereas the optical detection signals output by the elements A and B and those output by the elements C and D each pair have a difference in phase of xcex94xcfx86. Therefore, first and second diagonal synthesized signals (A+D) and (B+C) each include the common phase difference (xcex94xcfx86). Also, when the second diagonal synthesized signal (B+C) is subtracted from the first diagonal synthesized signal (A+D), the common phase difference (xcex94xcfx86) is deleted. Thus, the phase difference hardly affects a tracking error.
FIGS. 3A through 3C illustrate phase relationships between optical detection signals obtained from the elements A through D, respectively, when an optical disk having a nonuniform pit depth is scanned in a radial direction.
In the case of the optical disk having a nonuniform pit depth, each pair of the optical detection signals output by the elements A and B and the elements C and D has a phase difference of xcex94xcfx86, and further has a group phase difference of xcex94xcex8 depending on a pit depth.
The first and second diagonal synthesized signals (A+D) and (B+C) each have different phase errors of xcex94xcfx86 and xcex94xcfx86+xcex94xcex8, so that distortion is generated. Thus, a normal tracking error signal is not obtained.
FIG. 4 is a block diagram showing a configuration of another conventional apparatus for generating a tracking error signal. The apparatus of FIG. 4 includes first through fourth delays 40, 42, 44, and 46, first and second adders 48 and 50, equalizers 52 and 54, and a phase detector 56.
The first through fourth delays 40, 42, 44 and 46 compensate for an optical signal detected by a four-element optical detector, each using a different delay amount.
The first adder 48 adds optical signals A and D respectively from the first and third delays 40 and 44 and outputs a first diagonal added signal (A+D). The second adder 50 adds optical signals B and C respectively from the second and fourth delays 42 and 46 and outputs a second diagonal added signal (B+C).
The equalizers 52 and 54 equalize the first and second diagonal added signals (A+D) and (B+C) from the first and second adders 48 and 50, respectively. The phase detector 56 determines a difference between the output signals of the equalizers 52 and 54 and outputs a tracking error signal ((A+D)xe2x88x92(13+C)).
Here, the first through fourth delays 40, 42, 44, and 46 delay the optical signals A, B, C and D output by the four-element optical detector, to prevent them from having a phase difference. The delay amount of each of the delays 40, 42, 44 and 46 uses a value measured by a system upon initial driving of an optical disk. That is, the system first detects the phase differences between the optical detection signals A, B, C and D of the four-element optical detector, and regulates the delay amount of each of the delays 40, 42, 44 and 46 to minimize the phase differences between the optical detection signals A, B, C and D, thereby driving loaded optical disks.
However, the conventional apparatus for generating a tracking error signal as shown in FIG. 4 requires a complicated algorithm for regulating the delay amounts of the delays 40, 42, 44 and 46, thus increasing a load to the system and power consumption.
To solve the above problems, it is an object of the present invention to provide an apparatus for adaptively generating a tracking error signal according to a phase error caused by a pit depth.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the present invention, there is provided an apparatus for generating a tracking error signal, including a first adder to output a first added signal (A+C) among optical detection signals A, B, C and D output by four respective elements for detecting light beams reflected by an optical disk; a second adder to output a second added signal (B+D) among the optical detection signals A, B, C and D; a multiplexer to receive the optical detection signals A, B, C and D, the first added signal (A+C), and the second added signal (B+D), and to select and output the signals (A+C) and (B+D), A and B, or C and D; a phase detector to determine a difference of the signals output by the multiplexer and output the difference as a tracking error signal and determine whether the tracking error signal is normal; and a selection controller to control selection of the multiplexer according to the result of the determination of the phase detector.